It may be desirable for an online merchant to offer promotions on products from time to time. As an example, an online merchant may offer a promotion on a product such that if a customer buys one of the product, the customer can get another one of the product for free. Another promotion may advertise that if the customer buys one of the product, the customer can receive fifty-percent off of one of another product. Many different types of promotions may be used, for example, to increase sales volume for the online merchant.